This simple,
yet critical aspect, is why any discussion of the A’s or Rays relocating
is a non-starter. Because without that, what you have are owners trying
to leverage a ballpark deal, first in their market, and then only with
the blessing of the league and a clear message that says, “Team up for
sale,” does relocation to a new market occur.

Brown also identifies the pesky Giants/Mariners TV rights issues, the lack of a suitable stadium option right now, and of course, the complete lack of funding for a future stadium.

And while Brown doesn't complete discount Portland as a possible future MLB market, he does contend plans are a loooong way from fruition:

It’s those damned details that are getting in the way of the fun.
Details that move efforts from “dream” to something closer to “reality.”
When I was first approached about this current effort, my biggest
advice was “work quietly behind the scenes.” That in doing so,
politicians, MLB, and owners like Lew Wolff would not be placed in an
uncomfortable spot of having to publically address MLB to Portland
before anything substantive had been pulled together.

As it was in 2003, so should it be now. When the Expos were up for
relocation, it provided Portland an opportunity to take a detailed
examination of the market and report the findings, regardless of what
club might actually land here one day. Focus on the “market viability”
not “baseball has a problem, and we have a solution that has no answers
to the major questions.” The former, not the latter, is where efforts to
bring MLB to Portland should be. Until then, the dream will likely
continue.